*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
body{
    background: #2d3436;
}
a{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    width: 180px;
    height: 50px;
    background: #2d3436;
    text-transform: uppercase;
    text-align: center;
    line-height: 45px;
    color: #ff0;
    text-decoration: none;
    font-size: 20px;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    letter-spacing: 4px;
    /* border: 3px solid #ffffff; */
}
a::before,
a::after,
span::before,
span::after{
    content: "";
    position: absolute;
    width: 10px;
    height: 10px;
    background: #ff0;
    transition: 1s;
    mix-blend-mode: hue;
}
a::before{
    top: -2px;
    left: -2px;
    border-top-left-radius: 1px;
}
a::after{
    top: -2px;
    right: -2px;
    border-top-right-radius: 1px;
}
span::before{
    bottom: -2px;
    left: -2px;
    border-bottom-left-radius: 1px;
}
span::after{
    bottom: -2px;
    right: -2px;
    border-bottom-right-radius: 1px;

}
a:hover:before,
a:hover:after,
a:hover span:before,
a:hover span:after{
    width: calc(180px/2);
    height: calc(50px/2);
}



